1. Field of the Invention
The present invention relates to loudspeakers. More specifically, the present invention relates to those loudspeakers with magnets enclosed in a housing.
2. Description of the Prior Art
Loudspeakers have always been unattractive, cumbersome affairs which have been susceptible to damage. Typically a loudspeaker includes a permanent magnet for generating a magnetic field, and a yoke consisting of pole and plate pieces for focusing the magnetic field to an air gap in which the field is particularly intensified. A voice coil is suspended in the air gap so as to be able to vibrate. A current is passed through the voice coil and the interaction of the magnetic field created by the current and the magnetic field from the permanent magnet causes the voice coil to vibrate. Attached to the voice coil is a diaphragm which has a large surface area to cause air in the vicinity of the diaphragm to vibrate, thus creating sound.
It is important that the voice coil be disposed in the center of the air gap and not touch the yoke so that the voice coil can vibrate freely. Accordingly, it is important that the relative positions of the pole pieces be rigidly fixed.
Typically, plate pieces have been glued or cemented to the permanent magnet. In this manner, the width of the air gap is rigidly set. However, problems exist with this arrangement. Typically, the permanent magnet is made of a material which chips easily. While the loudspeaker is being assembled and during use of the loudspeaker, it is easy for the permanent magnet to become chipped. Also, the glue cementing the plate pieces to the permanent magnet has been known to form an inadequate bond so that the yoke separates from the magnet.
To overcome these problems, the permanent magnet and yoke have been enclosed or encapsulated in plastic or the like. Encapsulation economically fixes the position of the yoke and permanent magnet in a manner that is aesthetically pleasing. Furthermore, enclosure or encapsulation prevents the permanent magnet from being chipped.
Typically, a non-magnetic rigid mounting plate is bolted to the enclosed magnet assembly. The diaphragm and the voice coil are attached to and suspended from the plate. Electrical leads from the voice coil are attached to terminals on the plate, to form a complete loudspeaker. The loudspeaker is then mounted to an enclosure forming a portion of a loudspeaker system.
Although such construction does reduce the structure necessary to position the yoke and the permanent magnet, the remainder of the structure tends to be bulky due to the necessity of the mounting plate. The mounting plate also detracts from the attractiveness of the loudspeaker package. Since the voice coil must be centered within the air gap, the operation of bolting the mounting plate to the enclosed assembly becomes critical, and thus time consuming and expensive.